This invention relates generally to the handling and storing of fiber optic communications cables, and more particularly an improved method and apparatus whereby the spliced optical fibers of the cable are conveniently stored, protected and organized.
The cable with which the present invention is concerned consists of a number of plastic buffer tubes which typically may be from five to ten in number. Each buffer tube contains from one to twelve optical fibers. In the cable proper the buffer tubes are stranded over a central strength member of steel wire or the like and covered by an outer jacket or sheath of polyethylene or polyvinyl chloride.
The optical fibers themselves are approximately 125.times.10.sup.-6 meters (0.005 inches) in diameter and contain a protective plastic coating which increases the diameter to 250.times.10.sup.-6 meters (0.010 inches). Prior to splicing one optical fiber with another the plastic coating is first removed to expose the glass. This may be done by immersing the fiber in a methylene chloride solution or by other conventional means. The exposed fibers are then trimmed with a suitable hand tool to insure that the ends of the fibers have a clean sharp cut. The two fibers to be spliced are placed in a fusion splicer and accurately aligned by a microscope following which an electric arc is discharged at the ends of the fibers to melt the glass and fuse the two fibers together. Prior to the splicing operation a protective sleeve is slid over one of the fibers and shifted to a position out of the way of the splice region, and after the splice is made the protective sleeve is slid over the splice to protect the same.
A typical buffer tube encases from six to twelve optical fibers. A length of each fiber of the order of about six inches projects outwardly from the buffer tube so as to be exposed for splicing and for mounting on a splice tray. The length of buffer tube extending from the splice tray to the sheath of the main cable may be of the order of fifteen to twenty feet to enable the splicing to be carried out at a remote location. This length must, however, be stored, organized, and protected. Moreover, the storage arrangement must be such that individual fibers can be addressed in the future if desired.
Various arrangements have been provided for organizing the exposed lengths of buffer tubing and the individual fibers. In general the individual fibers are organized by putting the splices into the protective sleeves, as aforesaid, and mounting the individual splices on a splice block which forms a permanent part of a tray. The tray keeps the fibers from being tangled and the tray also holds the fibers in a manner to insure that the minimum bend radius of the glass fiber is not exceeded. The buffer tubing may be wrapped about the tray and/or stored in a compartment in a splice box.
On large fiber cables, more than one tray is employed, for example one tray for each group of fibers in a buffer tube. A standard procedure of organizing the various trays is to place them in stacked relationship in a receptacle, which is thereafter closed and placed underground. To facilitate recovery of the stacked trays it is sometimes desired to place the receptacle in a closure called a "hand hole". This is a large box which is used to store the receptacle underground without having to surround completely the receptacle with dirt. The hand hole is covered with about six inches of dirt, and the cable is buried about thirty inches deep. To get at the cable only six inches of dirt need be removed to obtain access to the lid of the hand hole.
In the foregoing arrangements the embodiment of the splice block as a permanent part of the tray inhibits the use of splice blocks of various sizes or configurations. For different splices a different splice tray must be used. This is in contrast to a convenient and smaller removable splice block which is used in the present invention. Moreover, when the stacked tray construction is used, it is frequently necessary to disturb one or more of the trays when access is sought to one or more of the other trays.